OBJECTIVES: Lipoprotein oxidation has been implicated in the pathogenesis of preeclampsia and paraoxonase, an antioxidant enzyme shown to protect lipoproteins from being oxidized. The aim of the present study was to evaluate oxidizability of apolipoprotein B-containing lipoproteins and serum paraoxonase/arylesterase activities in preeclampsia. DESIGN AND METHODS: Twenty-one women with mild preeclampsia, 21 women with severe preeclampsia, and 20 women with normal uncomplicated pregnancy were included in this study. Serum malondialdehyde (MDA) level, an indicator of lipid peroxidation, was measured by high-performance liquid chromatography (HPLC). The oxidizability of apolipoprotein B-containing lipoproteins was evaluated by copper-induced in vitro peroxidation of the isolated fraction of apolipoprotein B-containing lipoproteins coupled with the thiobarbituric acid-reactive substances assay and expressed as the difference between copper-treated MDA and basal MDA (DeltaMDA). The serum paraoxonase and arylesterase activities were determined spectrophotometrically. RESULTS: Serum MDA and DeltaMDA levels of apolipoprotein B-containing lipoproteins were significantly higher in both mild and severe preeclampsia groups than in the normal pregnant group. Serum paraoxonase and arylesterase activities were not significantly different among the study groups. CONCLUSIONS: Enhancement in oxidizability of apolipoprotein B-containing lipoproteins accompanying with dyslipidemia and increased serum MDA levels suggests that those lipoproteins play a role in the pathogenesis of preeclampsia. Further studies are needed to investigate serum paraoxonase activity in women with normal pregnancies and preeclampsia.